U.S. patent number 5,770,478 [Application Number 08/837,497] was granted by the patent office on 1998-06-23 for integral mesh flat plate cooling method.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Sushumna Iruvanti, Martin Klepeis, Gaetano Paolo Messina, Raed Sherif.
United States Patent |
5,770,478 |
Iruvanti , et al. |
June 23, 1998 |
Integral mesh flat plate cooling method
Abstract
An electronic module is provided comprising integrated circuit
chips mounted on a substrate and having a specially designed
cooling plate overlying the chip producing a gap above about 1 mil
and a thermal paste or thermal adhesive between the cooling plate
and the chip to facilitate heat transfer from the chip to the
cooling plate. The cooling plate has a roughened area made by grit
blasting and the like and having a roughness of about 0.4 to 6.4
microns or comprising a plurality of channels and corresponding
protrusions overlying the chip area which roughened area penetrates
the thermal paste and thermal adhesive and improves the adhesion
and inhibits the flow of thermal paste from between the lower
surface of the cooling plate and the upper surface of the chip
during operation of the electronic module. A preferred cooling
plate comprises a bead blasted roughened surface or plurality of
criss-crossing channels forming protrusions having a width of less
than about 1 mm and a channel width of about 1 mm to 5 mm.
Inventors: |
Iruvanti; Sushumna (Wappingers
Falls, NY), Klepeis; Martin (Poughkeepsie, NY), Messina;
Gaetano Paolo (Hopewell Junction, NY), Sherif; Raed
(Croton, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
25053132 |
Appl.
No.: |
08/837,497 |
Filed: |
April 7, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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758789 |
Dec 3, 1996 |
|
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|
Current U.S.
Class: |
438/122;
257/E23.103; 257/E25.012; 438/118; 438/54 |
Current CPC
Class: |
H01L
21/4878 (20130101); H01L 23/3672 (20130101); H01L
25/0655 (20130101); H01L 24/83 (20130101); H01L
2224/73253 (20130101); H01L 2924/09701 (20130101); H01L
2224/16225 (20130101); H01L 2224/32245 (20130101); H01L
2224/83385 (20130101); H01L 2924/14 (20130101); H01L
2924/14 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
H01L
21/02 (20060101); H01L 21/48 (20060101); H01L
23/34 (20060101); H01L 23/367 (20060101); H01L
25/065 (20060101); H01L 021/60 (); H01L
021/00 () |
Field of
Search: |
;438/122,54,118 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Jackson; Jerome
Assistant Examiner: Arroyo; Teresa M.
Attorney, Agent or Firm: DeLio & Peterson, LLC
Tomaszewski; John J. Ahsan; Aziz M.
Parent Case Text
This is a divisional of copending application(s) Ser. No.
08/758,789 filed on Dec. 3, 1996.
Claims
Thus, having described the invention, what is claimed is:
1. A method for cooling at least one integrated circuit chip
mounted on a substrate comprising:
providing a substrate having at least one chip mounted thereon;
providing a cooling plate overlying the substrate and the chip;
providing a thermal paste or thermal adhesive between an upper
surface of the chip and a lower surface of the cooling plate
wherein the thickness of the paste or adhesive is above about 1
mil;
wherein the lower surface of the cooling plate has a roughened
surface wherein the roughened surface comprises channels which
channels form a plurality of corresponding protrusions which
roughened surface penetrates and improves the adhesion of the
thermal paste and/or thermal conductive adhesive and inhibits the
flow of thermal paste from between the upper surface of the chip
and the lower surface of the cooling plate.
2. The method of claim 1 wherein the ratio of the width of the
protrusion to the width of the channel is about 2:1 to 1:10 and the
protrusions are a plurality of parallel protrusions.
3. The method of claim 1 wherein the parallel protrusions have a
width less than about 1 mm.
4. The method of claim 2 wherein the protrusions are discrete and
are formed by a plurality of criss-crossing channels.
5. The method of claim 4 wherein the protrusions have a width less
than about 1 mm.
6. The method of claim 2 wherein the periphery of the roughened
area which periphery overlies only the periphery of the chip.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electronic module having enhanced
module cooling properties and to a method for cooling the module
and, in particular, to an electronic hermetically sealed module
comprising an integrated circuit chip and a relatively thick
thermal paste sandwiched in a gap between the chip and a specially
designed overlying cooling plate having a roughened surface by grit
blasting, etc. or having a plurality of channels or grooves forming
a corresponding plurality of protrusions which are either co-planar
with the surface of the plate or which extend above the surface of
the plate and which roughened surface penetrates the paste and
inhibit the flow of paste from between the chip and the cooling
plate.
2. Description of Related Art
Integrated circuit chips mounted on substrates and particularly in
an array on the substrate present special cooling difficulties.
While chip size has increased over the years and power usage is
more efficient than in the past, new cooling systems are still
needed to remove the relatively high power density generated by the
chips. The prior art is replete with different types of multi-chip
modules (MCM's) designed to enclose and cool integrated circuit
chips mounted on ceramic-glass substrates. In some instances, the
MCM's utilize liquid coolants to cool the chips such as those
described in U.S. Pat. Nos. 5,239,200; 5,294,893 and 5,177,667.
Another approach to cooling has been described in U.S. Pat. No.
4,500,945 by the use of liquid cooled pistons contacting the chips
within the MCM's to remove heat.
Another approach to cooling chips in MCM's has been to utilize a
thermally conductive medium, such as high thermal conductivity
paste, between the top of the integrated circuit chip mounted on
the substrate and the lower surface of a cooling plate facing the
substrate. An example of the useful, stable, high solid content,
high thermal conductivity paste is disclosed in U.S. Pat. No.
5,098,609 to Iruvanti et al., which patent is hereby incorporated
by reference. This compound is applied as a thin film in the gap
between the top of the chip and the lower surface of the plate of
the MCM. In order to properly control the amount of heat removed
from the integrated circuit chip, it is desirable to determine a
gap of the desired distance between the top of the chip and the
lower surface of the plate and to fill that space completely with
thermally conductive mediums such as the aforementioned paste.
U.S. Pat. No. 5,345,107 to Daikoku et al. discloses a cooling
apparatus for an electronic device in which a cooling solid body is
provided on its one surface with a number of grooves. The grooves
on the cooling plate are disclosed to retain the thermal conductive
grease therein so that the thermal conductive grease does not swell
to the outside of contact surfaces of the electronic device and the
cooling solid body. The capacity of the grooves is disclosed to be
larger than the volume of the thermal grease applied between the
chip and the cooling surface. It is further disclosed that the
cooling plate surface have grooves which communicate with the
outside of the chip surface and/or have a through hole in the
cooling plate surface for communication with the outside
environment for plate designs where the grooves do not extend to
the outside or past the outside of the chip surface. Typical
cooling plates of the patent show grooves having a 1 mm width and a
groove pitch of about 6 mm to grooves having a 0.5 mm width with a
groove pitch of 1.5 mm. The high thermal conductive grease was also
disclosed as being about 1 mil to 4 mil thick. The disclosure of
the above patent is hereby incorporated by reference.
U.S. Pat. No. 4,823,863 shows a thermal conduction device having a
porous surface layer. A thermal paste is not employed and a liquid
such as oil is contained in the cavities of the porous layer and
the chip and cooling plate are held in close contact by the surface
tension of the oil.
Many modules especially hermetically sealed modules however, now
use thicker gaps above 2 mils generally about 7-9 mils and even up
to 15 mil and higher. This has created problems with the
effectiveness of the cooling because the thermal paste slips out of
the gap due to gravity and/or power cycling or power aging during
use of the module.
Bearing in mind the problems and deficiencies of the prior art, it
is therefore an object of the present invention to provide a method
for improving retention of a thermal paste or other such heat
transfer medium such as a thermally conductive adhesive between a
thermal conducting plate and an integrated circuit chip of an
electronic module during power cycling or power aging which occurs
during module operating conditions.
It is a further object of the invention to provide electronic
modules including large multichip modules (MCM's) utilizing a
thermal paste for heat transfer and where thermal paste slippage is
a serious problem due to thermal mechanically induced gap changes
which are pronounced due to the nature of the module.
It is yet another object of the present invention to provide a
cooling plate for use in electronic modules which utilize a thermal
paste between the chip surface and the cooling plate surface of the
electronic module.
It is still a further object of the invention to provide electronic
modules having large gaps above about 4 mils between the chip
surface and cooling plate surface in which a thermal paste is
employed as a heat transfer medium to cool the chip.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects, which will be apparent to those
skilled in the art, are achieved in the present invention which is
directed in a first aspect to an electronic module comprising:
a substrate having at least one integrated circuit chip attached
thereto;
a cooling plate overlying the substrate and the chip and forming a
gap above about 1 mil when using a thermal adhesive and preferably
above about 2 mils when using a thermal paste between the upper
surface of the chip and lower surface of the plate; and
a thermally conductive paste or thermally conductive adhesive
between the upper surface of the chip and lower surface of the
cooling plate;
wherein the cooling plate has a roughened lower surface formed by,
e.g., bead blasting or comprising a plurality of specially defined
channels in the lower surface of the cooling plate which channels
form corresponding protrusions which are either co-planar with the
surface of the plate or which extend above the surface of the plate
and which roughened surface penetrates the thermal paste and
inhibits the flow of thermal paste from between the chip surface
and the thermal plate. Preferably the ratio of the width of the
protrusion to the width of the channel is about 1:1 or lower and
more preferably, the protrusions have a width less than about 1
mm.
The roughened cooling plate surface may be formed by, e.g., grit
blasting, bead blasting or chemical etching to provide a textured
surface characterized by having a multiplicity of randomly sized
peaks and valleys wherein the surface has peaks of about 0.4 to 6.4
microns as measured by roughness instruments such as an optical
scanning instrument.
In another aspect of the invention, a method for cooling at least
one integrated circuit chip mounted on a substrate comprises:
providing a substrate having at least one integrated circuit chip
mounted thereon;
providing a cooling plate overlying the substrate and the chip
wherein a gap above about 1 mils when using a thermal adhesive and
preferably above about 2 mils when using a thermal paste, is formed
between the upper surface of the chip and lower surface of the
plate;
providing a thermal paste or thermal conducting adhesive between
the upper surface of the chip and the lower surface of cooling
plate;
wherein the lower surface of the cooling plate has a roughened
surface formed by e.g., bead blasting or comprising a plurality of
specially defined channels in the lower surface of the cooling
plate which channels form corresponding protrusions which are
either co-planar with the surface of the plate or extend above the
surface of the plate and which roughened surface penetrates and
improves adhesion of the thermal paste and/or thermal conductive
adhesive and inhibits the flow of thermal paste from between the
chip surface and the lower surface of the thermal plate. Preferably
the ratio of the width of the protrusion to the width of the
channel is about 1:1 or lower and more preferably wherein the
protrusions have a width less than about 1 mm.
For a roughened surface characterized by a textured surface having
a multiplicity of peaks and valleys the surface has peaks of about
0.4 to 6.4 microns high.
In a further aspect of the present invention, a cooling plate is
provided for use in electronic modules to overlie integrated
circuit chips and in which a thermal paste or thermal adhesive is
employed between the upper surface of the integrated circuit chip
and the lower surface of the cooling plate at a thickness of about
1 mil and higher to provide a heat transfer medium to remove heat
generated by the integrated circuit chip.
The cooling plate has a roughened surface which inhibits the flow
of thermal paste from between the chip surface and the thermal
plate. The roughened surface of the cooling plate may be made by
any of a variety of techniques such as by end milling or chemical
etching using photolithographic techniques for channeled surfaces.
A roughened surface comprising grooves in the surface of the plate
has corresponding protrusions formed by the grooves which are
either co-planar with the surface of the plate or which extend
above the surface of the plate and which penetrate the thermal
paste when the plate overlies the chip. The channels and
protrusions are typically in X and/or Y directions generally
parallel to the chip edges or in criss-crossing arrangement at any
angle, typically orthogonal. The protrusions may overlie only the
area corresponding to the chip area or the protrusions may cover
the complete surface of the cooling plate for ease of manufacture
and use. It is important that the protrusions in the cooling plate
be integral with the plate and that the size of the protrusions be
specially correlated with the size of the channels to provide the
enhanced thermal paste retention effects of the invention.
Roughened surfaces produced by, e.g., grit blasting, bead blasting
or chemical etching typically have a roughness comprising peaks and
valleys wherein the peaks are about 0.4 to 6.4 microns, preferably
0.8 to 3.2 microns, e.g., 1.6 to 3.2 microns. These values
represent average values of the textured roughened surface
typically defined as R.sub.a - the root mean squared average. The
roughened surface has a plurality of peaks and valleys produced by
the etching or blasting method with the height of the peaks being
the aforementioned range of about 0.4 to 6.4 microns. As well known
to those skilled in the art such roughened surfaces have a texture
such as sandpaper comprising extremely small protrusions of the
metal randomly distributed on the surface of the cooling plate,
which protrusions are formed by the blasting or chemical etching
process.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the invention believed to be novel and the elements
characteristic of the invention are set forth with particularity in
the appended claims. The figures are for illustration purposes only
and are not drawn to scale. The invention itself, however, both as
to organization and method of operation, may best be understood by
reference to the detailed description which follows taken in
conjunction with the accompanying drawings in which:
FIG. 1 is a side elevational cross-sectional view of a portion of a
multi-chip module of the invention.
FIG. 2 is an enlarged view of section A of the multi-chip module of
the invention shown in FIG. 1.
FIG. 3 is a top plan view of the lower surface of a cooling plate
of the invention.
FIG. 4 is an enlarged view of section B of the cooling plate of
FIG. 3.
FIGS. 5, 6 and 7 are an enlarged views of roughened surfaces of
cooling plates of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
In describing the preferred embodiment of the present invention,
reference will be made herein to FIGS. 1-7 of the drawings in which
like numerals refer to like features of the invention. Features of
the invention are not necessarily shown to scale in the
drawings.
In FIG. 1, there is shown an electronic module 10 of the invention.
The module comprises a substrate 11 having a chip 13 attached
thereto by solder connections 12. Typically, the integrated circuit
chips 13 are arranged in an array, such as a 5.times.5 array, on
the top surface of substrate 11. The chips 13 are electrically
connected to the substrate by a plurality of solder connections 12
which is well known in the art as "flip chip" packaging. The lower
surface of the substrate 11 may contain connectors (not shown) for
connection of the module to a circuit board within a mainframe
computer or other electronic device.
A thermal cooling plate 14 is shown overlying the substrate and
chip. The cooling plate may be any of the well-known devices
generally referred to as hats or caps and the hat is generally a
solid flat piece of metal or ceramic. A heat sink or cold plate is
generally placed on top of the hat and may have a coolant inlet and
a coolant outlet for removing heat from the hat and the module.
Typically, a coolant such as water, is passed through the cold
plate or air passed over the heat sink to remove the heat generated
by chip 13. The cooling plate 14 may be made from any suitable
material such as aluminum, copper, ceramic or components such as
CuW or Al SiC.
Sandwiched between the upper surface of chip 13 and the lower
surface of cooling plate 14 is a thermal conductive paste 15. The
thermal conductive paste is generally provided in the form of thin
film or layer covering substantially all of the top surface of chip
13 and sandwiched between top surface of chip 13 and the lower
surface of plate 14. The preferred thermally conductive medium is a
paste such as that disclosed in the aforementioned U.S. Pat. No.
5,098,609. The thickness of the thermal paste 15 is preestablished
by design in order to optimize the heat removal from chip 13 during
operation of the electronic module. The thickness of the paste for
electronic modules contemplated herein will be typically above
about 1 mil usually 4 mils to 15 mils and this range may vary
widely depending on the electronic module and cooling results
desired. The roughness of the cooling plate 14 surface is shown
generally as 16 and preferably comprises either a grit or bead
blasted surface or a plurality of grooves (and corresponding formed
protrusions) in the cooling plate surface as more fully described
hereinbelow.
FIG. 2 is an enlarged view of section A of FIG. 1 showing in detail
the channels 18 and corresponding protrusions 17 of roughened area
16. The protrusions 17 have a height H and the protrusions
penetrate the thermal paste 15 and provide an inhibiting effect to
the flow of the thermal paste from between the upper surface 13a of
chip 13 and the lower surface 14a of cooling plate 14. The width of
the protrusion 17 is shown as W and the width of the channel 18 is
shown as C.
In FIG. 3, the lower surface of cooling plate 14 is shown having
four roughened areas 16. These four roughened areas would overly
four integrated circuit chips 13 in a MCM and it will be
appreciated that different cooling plate designs may be employed
depending on the chip configuration on the substrate. The roughened
areas 16 comprise parallel channels and the resulting protrusions
described below and these protrusions as shown in FIG. 2 would
penetrate the paste 15 and provide an adhesive effect to prevent
slippage of the thermal paste 15 from between the upper chip
surface 13a and lower surface 14a of cooling plate 14.
FIG. 4 shows an enlarged view of section B of FIG. 3 and the
cooling plate 14 can be seen to have a plurality of staggered
channels 18 and the resulting protrusions 17 formed between the
channels. Preferably the upper surface of the protrusion 17 is
coplanar with the surface of the plate 14 so that there is no
communication of the grooves 18 with the area outside the chip
area.
Different designs can be employed for the channels 18 and
protrusions 17 of cooling plate 14.
In FIG. 5 a cooling plate 14 is shown wherein the surface of the
plate has a plurality of criss-crossing integral protrusions 17
forming a grid. Thus, the protrusions 17 bound a plurality of open
valley areas 18 interspersed between the grid protrusion 17. The
protrusion would penetrate the thermal paste as shown in FIG. 2 and
would inhibit the thermal paste from flowing out between the chip
and cooling plate.
In FIG. 6 a cooling plate 14 is shown having a plurality of
channels 18 crossing at right angles forming discrete protrusions
17. In FIG. 7 a cooling plate 14 is shown wherein rows 20 and
columns 19 have staggered protrusions 17 and valley areas 18,
forming a checkerboard configuration.
It is a preferred feature of the invention that the width of the
protrusions(W) and the width of the channels (C) be specially
correlated. Broadly stated, the width of the protrusion is
preferably the same or smaller than the width of the channel. It is
also preferred that the width of the protrusion be less than about
1 mm and preferably have a height H of about 10% to 60%, e.g.,
15-50% of the thickness of the thermal paste. The width of the
protrusions may vary widely preferably below about 1 mm depending
on the use of the module and/or thermal paste used, and is
preferably about 0.05 to 0.5 mm. The ratio of the width of the
protrusion to the width of the channel is preferably less than
about 2:1 to 1:10, most preferably 1:1 to 1:3. The width of the
protrusion is defined as the larger peripheral dimension of the
protrusion when the protrusion is in the form of a rectangle. For
circular or other such shape protrusions, the diameter of the shape
is considered its width. Variable width protrusions and channels in
the same roughened area, are also contemplated to be within the
invention.
For cooling plates having surfaces textured or roughened by grit or
bead blasting or other means, the surface of the plate has a
multiplicity of peaks and valleys wherein the surface has peaks of
about 0.4 to 6.4 microns, preferably about 0.8 to 3.2 and e.g., 1.6
to 3.2 microns. The width of the peaks and valleys is also
generally about the same size as the peaks.
While the present invention has been particularly described, in
conjunction with a specific preferred embodiment, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. It is therefore contemplated that the appended claims
will embrace any such alternatives, modifications and variations as
falling within the true scope and spirit of the present
invention.
* * * * *